4 years ago I moved overseas and parked the Z. Before I did that, i picked up a 231C with a floor shifter for close to nothing and planned on swapping that in the Z one day and doing a mild SAS to keep it road friendly. I am moving back this summer and the Z will never see the road again. So my questions/observations/thoughts are this:looking at D60/14BFF set up. Keeping the 4.3 (auto) because I'm a slow crawler and not much for the skinny pedal. I was thinking about making the 231 a doubler and throwing a dana 300 or maybe a 1-ton t-case out of a full-size (241??? can't remember) But then I thought about putting the 231 in there just as it is and running a divorced t-case behind it that is pass drop...

But then I thought, why not just make the 233 a doubler and mate the 231 on it.

I know thats a lot of options out there. I won't even get to the states for another 2 months and probably won't touch the truck for another year. Just picking some brains.

This question got me thinking... And reading.... I still have a lot of both to do....

But, I have learned that if you have a 27 spline input and output on the transfer cases, you can slide the 2 transfer cases together. What I'm curious about is using a 233 for the doubler and a 231 as the actual transfer case and getting a neutral in there somewhere, since you can't put a 233 in neutral.

Post up what ever else you find. This would be a great addition to my s10 when I swap in my axles.

Yeah, I will need to fab up an adapter plate to slide the two cases together and chop off half of the case to clear for the front output of the 231. I know a doubler isn't a huge advantage for an automatic compared to a stick, but I feel it will make wheeling a little easier on my tranny and be fun to fab/play with. I don't know the spline counts and I can't count them yet being I'm not in the US yet. I know the 231 I have came out of a 1st gen 4-door blazer and I have the rear slip-yoke and it has the fixed front yoke. It might be a different spline count but I'm not sure.

Our stock transfer case is an NP233C with 27 spline input, 32 spline output, and a 4 gear planetary. An np231c will swap in place of the np233c.

Np241c and np243c came in full size Chevy trucks. They came in 27 or 32 spline input, 32 spline output, and a 6 gear planetary. The planetaries are swappable into the smaller cases (ie, np233c). The planetaries have a different cut on the gears depending on what year, new style versus old style. Input gears are swappable.

There is a rare version of the np231c with 27 spline rear output. It would be ideal for what I have in mind...

The tech is basically the same, just different transfer cases (np207).

My thinking is....

S10 np231c, cut it in half, get some aluminum plate, take off the tail housing, fab up the "adapter" for np233c (just like in the link), cut off the end of the shaft to fit. This case will be the high low box, and *should have a neutral (I don't know np231c shift pattern).

Stock np233c that is in the truck (or whatever np2xx case you want) would need a 32 spline input swapped in, preferably with a 6 gear planetary with the correct cut (new vs. old cut).

What this essentially would accomplish is a level for H, N, L, which can be put in an s truck with stock interior parts. The np233c would still work with the push buttons as it is stock, all I can see needing to do is lengthen wires and breather hoses.

Other things you can do to the np233c is swap in the front output from a jeep or dodge or early s10 np231. You can also get a slip yoke eliminator (sye). Our transfer cases should have the wide chain already.

Now, what I do not know is if the 32 spline output from the transfer case will slip into a 32 spline input. This jargon is all dependent on that 1 key detail. According to the above link, we *should be able to do this easily with the 27 spline rear output, but it's rare.

If all this isn't enough options, there is an adapter to put the full size Chevy cases behind our transmissions, and we can even make an np243c work with our push buttons.

In theory, with enough room, you could run as many transfer cases as you want. Our wheelbase is long enough we should be able to get away with 2 easily.

I've been thinking about this all day....lol. I am going to try to find some parts and see what I can come up with, but it won't be anytime soon. I'd love to get something like this figured out before I swap my axles.

Please give me some thoughts on all this. There are also doubler kits available to make mating the 2 transfer cases together easier and shorter (just about any combo imaginable is doable), but I'd like to do something a little more, uh, budget....

That is exactly what I am thinking about doing, except leaving the 233 where it is and cutting/fabbing it and placing the 231 behind it because it already has the fixed front yoke (super budget!!!). If I was in Texas I would go see if my 231c has neutral or not. I don't remember there being a neutral but I'm not 100% sure.

On one forum I read that the 231 is easier to make into a doubler.. But no one ever said why. And I have seen a lot of kits to double a 231 and never seen a kit to double a 233. Do you have any idea why?

Thanks for the info!!! Please share whatever you find and I will do the same!

The reason no one talks about using the 233 in the front is because it's just simpler to not deal with the wiring. The main difference between a 231 and a 233 is the last digit, 1 for manual, 3 for electric shift. The same applies for the 241/243 combo. It's essentially the same transfer case. The reason I'd like to find a 231 for the first case is because I can use all factory parts to put it in, shifter, console, ect. It'd be a clean install. It would have the push buttons in place for the 233 and the lever for the 231. As far as you using the 231 because of the fixed yoke, if you open it up to put in the 6 gear planetary, you may as well just swap the fixed yoke into the 233 and cut the 231 in half. I have a Dakota 231 for the fixed yoke, and to my suprise, the 6 gear planetary I have on the shelf was a 32 spline. All I need now is the 231c, trams adapter, shifter, console, and another 6 gear planetary. I may try to find another 233 so I can get it all together without taking my tcase out.

Good info! Are you saying the 233 has the 6-gear planetary and the 231 does not? Is it necessary to put in the planetary gears in the 231? What does it have for reduction right now? I may be totally lost... let me know if I am. haha.

The 231 and 233 should have either a 3 or 4 gear planetary. The 6 gear planetary came in the bigger cases, 241, 243, ect. It's a direct swap. People claim they are stronger. To do what I'm going to attempt, you would need to find an input with 32 splines, and to get it out of another transfer case, you'd have to pull the planetary anyways, so may as well swap it if you can get the parts cheap and easy.

I've come to another issue with this. Crewcab rabbit (on s10forum) has a 231/233 doubler. In his build thread, he said his transmission went into limp mode when in double low. I never saw him say what the solution was.

So in the original post you said you want to go 60/14 bolt. You know gm Dana 60's are passenger side drop, right? You would need an np241 from an 89-91 k5 or suburban to get passenger side drop with a vss sensor. Unless you want to go sky high with huge tires, you may want to consider staying driver side drop with a ford or jeep axle. Full width axles with h2 wheels is a good looking combo.

On another note, I found a guy with a bunch of transfer cases. Now, to find time to go see what he has...

I plan on using ford kingpin 60. I dabble I military vehicles so getting my hands on some H1 rim with bead lock inserts should be really easy. Then I can recenter them and go from there. The truck will be a trailer queen so vss, abs, etc... doesn't matter.

Post. Some pics and info of your pillaging! Hope you have good pickings!

Iam running a clamp on tone ring from Advanced adapters and I put that on the tail shaft of the trans and drilled and taped the t case adaptor for the vss , truck wil shift wright in double low speedo just reads fast in low or double low , but at least the trans has more them manual 1-2